[tsimionescu]

Currently imaginable fusion power plants generate nowhere near enough power for the excess to be visible from outer space. They would not even be a blip compared to the largest already existing hydro power plant, for example.

Edit: to add some numbers, the "planned" DEMO power plant (the hypothetical successor of a successful ITER experiment) would produce something like 750MW, while Three Gorges Dam produces 22,500MW. Even if DEMO could be scaled up (which is hard, given that it would already be beyond the limits of today's material science), it definitely couldn't scale up 30 times.

[leereeves]

What stops fusion from scaling up by building more plants instead of larger plants?

[tsimionescu]

Nothing except the costs, but then it's not a single reactor anymore and other power plants scale as or more easily. So nothing is really special about fusion power if we just want to scale horizontally.

[leereeves]

I thought fusion is special because the inputs are more abundant and the outputs less toxic than other fuel power plants.

[tsimionescu]

Fusion can be compared like this:

- vs fossil fuels, almost limitless fuel with no greenhouse gas emissions

- vs nuclear fission, more fuel compared to current designs (though breeder reactors could essentially use any piece of rock as fuel), and shorter lived but even more toxic outputs (at least for D-T fusion, all pieces of the reactor become highly radioactive materials after 10-20 years)

- vs renewables, it has the advantage of being decoupled from weather and day/night patterns, but it is more expensive, it requires fuel, and it produces much more toxic outputs